The objective of this proposal is to characterize the structures of H-2 antigens. This study will focus primarily on the conformations of the membrane-bound glycoproteins coded for by H-2k and H-2K regions of the major histocompatibility complex of the mouse. The research plan will be directed in essentially four areas: 1) Several methods will be tested for improving the yields and separation of H-2b antigens as presently isolated in highly purified form from EL-4 cells by a purification scheme developed, in part, by the Principal Investigator. The aim here is to purify H-2b antigens from this lymphocytic leukemia-derived cell line for structural examination by conformationally sensitive spectroscopic probes, such as circular dichroism and fluorescence, and by amino acid composition and sequence analysis. 2) In an extension of current studies by the Principal Investigator, various molecules with public antigenic specificities of the H-2.28 family will be compared by tryptic peptide map analysis. The aim is to clarify the structural basis of this complex family of antigens which has recently led to the discovery of a new class of H-2D antigens. 3) The nature of the antigenic sites of H-2 antigens will be explored by chemical reagents which alter serological reactivity. Peptides protected from modification by specific alloantibody, and therefore presumably in or near antigenic sites, will be identified by tryptic peptide mapping techniques.